This invention relates to pumps of a small size particularly though not exclusively implantable pumps which are sufficiently small for use within the human body.
Pumps of small dimensions are used in implantable drug dispensing divices where a medicament is to be dispensed to an ambulatory patient on a regular or intermittent basis over an extended period of time, as where insulin is dispensed in the treatment of diabetes, or where chemotherapeutic drugs are dispersed in the treatment of cancer. In these circumstances it is advantageous in the treatment with the drug to perform an automatic dispensation of the drug without having to rely upon pills or injections. Thus a unit is implated within the patient comprising a reservoir of the drug and a pump, the pump being under control of a control circuit which may be coupled by an electromagnetic transmitter and receiver to an external control source.
Such a device for delivering the drug must be reliable in operation, sealed against body fluids and must hold a sufficient quantity of medication so as to avoid the need for frequent refills and must be refillable when empty. Furthermore, such dispensing systems must be physically small so as to be readily implatable without unnecessary disturbance of the body.
It is known to employ in such dispensing devices pumps such as the peristaltic type or solenoid type. Peristaltic pumps operate by responding to blood pressure within the body and solenoid pumps operate under control of an internal battery connected to a solenoid for operating a suitable pump mechanism. However such pumps are relatively large, and considering their size, are inefficient within the context of implantable units.